1. Field of the Invention
This invention relates, broadly speaking, to improvements in apparatus and method for extruding material. More specifically, this invention relates to apparatus and method for producing tubing from a pierced billet.
2. Description of the Prior Art
Many methods and apparatus for making tubing are well known, such as the conventional tube making by drawing technique.
Another conventional technique for making tubing involves filling the hole of a pierced billet with a plug, and thereafter reducing by extrusion the diameter of the composite structure, the difficulty in this method being the removal of the plug from the hole after extrusion.
U.S. Pat. No. 3,362,208 (1968) to Murphy discloses method and apparatus for making tubing wherein a solid (i.e., unperforated) billet is placed in a chamber adjacent a flat die with a cylindrical throat, a mandrel is forced through the chamber into and through the billet and into the throat of the die so as to provide a cylindrical annular passageway between the tip of the mandrel and the die. Thereafter, a ram is advanced into the chamber, surrounding the mandrel, and forcing the billet material through the annular passageway between the tip of the mandrel and the die to produce tubing. Means are provided to maintain the mandrel tip in the die against forces tending to expel the mandrel tip from the die.
U.S. Pat. 2,415,696 (1947) to Klocke discloses method and apparatus for making tubing wherein a solid (i.e., unperforated) billet is placed in a chamber above a die, a punch or mandrel is forced through the chamber into and through the billet and into the die (there being clearance between the die aperture and the punch so as to provide an annular opening through which annular opening some of the billet material is extruded as tubing), and thereafter the chamber is moved down over the die thereby further advancing the punch into the die and the billet through the annular opening to increase the length of tubing produced.